While there is a general and continuing desire to provide for ever increasing data storage capacities by individual hard disk drive systems, other general desires include the reduction of power consumption and the concomitant requirement for adequate heat dissipation capacity. The reasons for desiring reduced power consumption differ depending on specific market forces. In computer systems employing very high performance hard disk drives, the issues involve not only the physical size, cost and support of high-capacity power supply subsystems, but also the mechanical and electrical consequences of large thermogradients within the disk drive arising from high levels of internal power dissipation.
At the other extreme, small computer systems typified by the so-called "portable" and "lap-top" personal computers require hard disk drive systems operation from limited capacity power supplies, such as batteries, and very limited allowable power dissipation due to the high-packing density of components within the computer and limited effectiveness, if not ineffectiveness, of air cooling by a heat dissipation fan.
There are a number of approaches that can be taken to reduce power consumption by a hard disk drive without compromise of its otherwise achievable operating performance. A simple approach is to power-down the hard disk drive whenever immediate access to the stored data is unnecessary. The benefit of this approach is, of course, that power consumption is reduced to zero for a substantial portion of the time that the remainder of the computer system is operating. Conversely, a significant if not substantial delay is incurred whenever data access is required. Further, power consumption during each power-up of the hard disk drive may exceed the power savings when sufficiently frequent hard disk drive accesses are required.
Another approach is to carefully manage the design and implementation of each of the drive subsystems to obtain a hard disk drive optimized for power consumption. For example, the use of a full step-per-track stepper motor in the implementation of the read/write head positioner subsystem will permit simple open-loop controlled track following without the consumption of power. Similarly, the use of a low-torque spin motor will typically obtain a higher energy efficiency for steady state operation, though incur a longer spin-up delay and limit both the disk mass span and the maximum acceptable level of read/write head to disk surface friction.
Another possibility for optimization includes the combined use of custom integration and CMOS logic circuitry wherever possible. The object is to effectively provide the required controller logic, including analog functionality, in as few packages as possible. The trade off is, of course, cost; cost being a substantial, if not controlling factor to commercial success. Further, the use of custom integrated circuits, due to greatly increased development lead time complexity, may actually result in the realization of limited control capability and thereby compromise or restrict the overall functionally of the hard disk drive system. Additionally, there is an inherent limit on the degree of power savings that can be achieved through the use of very high levels of integration.